1. Field of the Invention
This invention relates to a two-dimensional image pickup apparatus and, more particularly, it relates to a two-dimensional image pickup apparatus adapted to read information originating from radiation such as radiation of X-rays.
2. Related Background Art
FIG. 1 of the accompanying drawings schematically illustrates a known image pickup apparatus adapted to X-ray photography and comprising a fluorescent member (e.g. scintillator) 1 operating as wavelength converter for converting X-rays 101 into rays within the sensible wavelength range of photoelectric converters 2a such as those of visible light, photoelectric converters 2a for converting the visible light into electric signals, a substrate 2b carrying the photoelectric converters 2a thereon, a base member 7 supporting the substrate 2b thereon, circuit boards 5a, 5b for processing electric signals produced by photoelectric conversion, wires connected to the circuit boards and an apparatus cabinet 8a containing the above components.
The substrate 2b arranged under the photoelectric converters 2a is typically made of glass because it is required to be free from chemical reactions with the semiconductor devices (such as the photoelectric converters) of the apparatus, resist the high temperature of the semiconductor forming process and maintain dimensional stability. The fluorescent member 1 is prepared by applying a fluorescent material of a metal compound to a resin plate and held in close contact with the substrate 2b. When the photoelectric converters 2a are required to be moisture-impermeable, the fluorescent member 1 and the photoelectric converters 2a may be hermetically sealed by a moisture-impermeable and X-ray transmissive film 6.
Typically a printed circuit board made of glass epoxy is used for the circuit board 5b on which electronic parts 5c are mounted, to meet the requirement of being easily available and hardly inflammable. These and other components are secured to the base member 7 by way of spacers 3a an 3b and then to the apparatus cabinet and hermetically closed by means of an X-ray transmissive closure 8b. 
In FIG. 1, reference symbol 3a denotes spacers arranged between the substrate 2b supporting the photoelectric converters and the base member 7 and reference symbol 3b denotes spacers arranged between the circuit board 5b and the base member 7, whereas reference symbol 5a denotes a flexible circuit board.
Such an image pickup apparatus is conventionally used for X-ray photography as a stationary apparatus. In recent years, there is an increasing demand for a lightweight, compact and portable image pickup apparatus adapted to rapid image pickup operations for producing fine images. However, with an apparatus having such a configuration, the heat generated by the electronic parts 5c is confined within the apparatus cabinet 8a to raise the internal temperature. Then, the temperature rise can by turn increase the internal noise and reduce the S/N ratio of the apparatus.
The use of a cooling system comprising one or more cooling fans (not shown) arranged in the apparatus cabinet 8a has been contemplated to sufficiently prevent such temperature rise from occuring in the inside. However, such an additional system can significantly increase the size and weight of the image pickup apparatus particularly because it requires pillars and a power source for driving the system.
In view of the above described circumstances, it is therefore an object of the present invention to provide a small, down-sized image pickup apparatus that is free from the above identified problems.
Another object of the present invention is to provide a two-dimensional image pickup apparatus adapted to stably reading information without significantly increasing the internal noise and reducing the S/N ratio if heat is generated by the electronic parts during the operation of the apparatus.
Still another object of the present invention is to provide an image pickup apparatus adapted to obtaining transmitted X-ray images for diagnosis and analysis.
Still another object of the present invention is to provide a low cost cassette-type image pickup apparatus that is small and lightweight and can be carried with ease.
According to an aspect of the invention, the above objects of the invention are achieved by providing a two-dimensional image pickup apparatus comprising two-dimensional photoelectric converters arranged on a substrate, a base member for supporting the substrate, electronic parts for processing the electric signals of said photoelectric converters and an apparatus cabinet containing the above components, said base member being formed by a metal-based printed circuit board, said electronic parts being mounted on said base member.
According to another aspect of the invention, in an image pickup apparatus according to the invention, said base member and part or all of said apparatus cabinet are formed by a metal-based printed circuit board and said electronic parts are mounted on said printed circuit board.